The present invention relates generally to preventing surge in compressors and more particularly for providing a method and means for providing antisurge protection for an installation having a dynamic compressor.
The main function of a control system for a dynamic compressor is to provide a control to protect the compressor and a user of a compressed gas from surge and its consequences. Generally, the intent of an antisurge system is to prevent the operating point of a compressor from approaching the surge limit by blowing-off or recirculating the part of the compressed gas. In order to achieve this, however, the surge control line must be set at a certain distance from the surge limit line.
In certain cases when the location of the surge limit line is not stable in time, even the best devices available which are designed to protect the compressor from approaching this limit on the field of a compressor performance map are not able to prevent surge. If the location of the surge limit on said map under a certain temperature and pressure of gas in the suction is known, then usually it is possible to define its new location when these conditions in suction change. But the location of a surge limit depends not only on temperature and pressure in the suction port, but it also depends upon the geometry of the running part of a compressor, the molecular composition of the gas, conditions in intermediate collers, etc. It is therefore very difficult, if not impossible, to take all of the important parameters into consideration. It is for this reason that all known compressor control systems which are designed to protect compressors from approaching a surge limit, and which take into consideration only certain conditions in suction, cannot always fulfill their task when the above mentioned conditions other than the parameters of a gas in the compressor's suction change.
Consequently, instead of attempting to prevent the approach of a compressor's operating point to an expected position of a surge limit, it would be desirable to protect a compressor from surge by the timely and proper measuring of certain surge parameters and using this information to activate a quick relief valve. It would also be desirable to be able to protect the user from interruptions or from considerable deviations of pressure or flow rate of a compressed gas, while at the same time protecting a compressor from surge.